1. Field of the Invention
The present invention relates to a polyvinyl alcohol polymer film which has small number of defects and is useful as a production raw material of a polarization film, and to a polarization film produced using this.
2. Description of the Prior Art
A polarizer having functions of transmission and shielding of light is a fundamental constituent element of a liquid crystal display (LCD), together with a liquid crystal having a function of switching light. This LCD is applied to portable apparatuses such as electronic calculators, wristwatches and the like in the initial period of development of LCD, and recently, to apparatuses in a wider range such as lap top personal computers, word processors, liquid crystal color projectors, navigation systems for automobiles, liquid crystal televisions, personal phones, indoor and outdoor measuring apparatuses and the like, and there is a need for polarizer having higher polarization characteristic and smaller defects than conventional products.
For obtaining a polarizer having general constitution, a polyvinyl alcohol polymer film (hereinafter, polyvinyl alcohol polymer is abbreviated as “PVA”, and a polyvinyl alcohol film is abbreviated as “PVA film” in some cases) is monoaxially stretched before dyeing, or dyed before monoaxial stretching, and subjected to fixing treatment with a boron compound (in some cases, dyeing and fixing treatment are conducted simultaneously, or monoaxial stretching and fixing treatment are conducted simultaneously), then, a protection film such as a triacetic cellulose (TAC) film, cellulose acetate butyrate (CAB) and the like is laminated on the polarization film.
By using the above-mentioned polarizer and liquid crystal having a function of switching light, dichroic display such as white and black display is enabled, and color display is realized by combination of a color filter. For improving color reproducibility of a liquid crystal display, more white hue and more black hue are required without using color filter, and for this, smaller unnecessary coloration on a polarizer is necessary.
However, when a PVA film is stretched, PVA in the PVA film may be partially dissolved in a dyeing process and a fixing treatment process with a boron compound in the case of dry stretching, and also in a swelling process before stretching and a stretching process in addition to the dyeing process and fixing treatment process in the case of wet stretching. The dissolved PVA is deposited in a vessel and adheres to a PVA film and polarization film, or deposited on a PVA film and polarization film, providing a defect, and consequently, decreases the yield of the polarization film. Further, dissolved PVA which has not been deposited causes expensive waste water treatment, problematically.
Furthermore, a conventional PVA film which is a raw material of a polarization film has a problem that unnecessary coloration tends to occur by conducting heat treatment in producing a polarization film. Particularly when a polarizer is made by a dry stretching method, unnecessary coloration such as yellowing and the like tends to occur. Therefore, a PVA film causing little unnecessary coloration even if heat treatment is effected in producing a polarization film has been desired to be realized.
Then, an object of the present invention is to provide a PVA film useful as a raw material for producing a polarization film having a small number of defects, and a polarization film made by using this PVA film.
Further, another object of the present invention is to provide a PVA film which causes little unnecessary coloration and is useful as a raw material of a polarization film, and a polarization film made by using this PVA film.